AR-15 101: A Complete Guide To Understanding How To Build An AR-15
AR Does Not Stand for Assault Rifle
Many believe that AR means assault rifle, but this is not true. AR stands for ArmaLite Rifle, which was the original manufacturer. In 1959 ArmaLite sold its rights to the AR-15 to Colt. In 1963 the Colt AR-15 Sporter was advertised as weighing only 6 pounds and being factory targeted at 100 yards, all for the price of $189.50.
The first AR-15 was adopted in 1962 by the United States Air Force for security police and received the designation M16. Semi-automatic AR-15s for sale to civilians are internally different from the fully automatic M16, even though they look identical on the outside.
In 1986 the Firearms Owners Protection Act redefined a machine gun. If you convert the AR-15 to a fully automatic weapon and are caught you will go to prison.
The lightweight design of the AR-15 makes it suitable for beginners. It has an excellent control layout and features an adjustable stock that allows its length to be adjusted for shooters of all sizes.
The steps to load and fire the rifle are simple and easy to learn. The rifle is soft shooting, with little recoil and a minimal blast with most loads. It is accurate and effective for several hundred yards.
The AR-15 can be easily stripped down to its base component groups for cleaning and oiling. It is easy for users to install custom parts to tailor the rifle to their needs. It will accept everything from free-floated handguards and enhanced action parts to muzzle devices.
The same rules apply whether building an AR-15 or purchasing a factory assembled gun. You do not need to be licensed or a gunsmith to build your own gun unless you are milling the lower receiver yourself.
There is no federal firearms registry. You do need to check the registry laws for the state you live in. If you are planning to sell the gun once it is built, then the same laws for private selling of firearms apply to self-built AR-15 rifles.
The AR platform is legal, but you will want to check the local, state, and federal laws to determine what parts you can legally buy to prevent violating a law. For example, in some areas, guns must have a fixed magazine.
Setting up Your AR-15 Workshop
You need an area set up for building and maintaining your AR-15. This starts with a good, solid workbench. Avoid a bench built of thin metal or fiberboard because you will need to mount a good vice onto it.
Next, you need a toolbox with plenty of drawers for organizing your tools, or a tool case with AR specific tools. An AR-15 Armorer’s Kit is a good item to have.
Regular tools such as wrenches and pliers are also necessary. You should have a screwdriver that accepts 1/4 inch bits, plus various standard bits. A standard flat-head screwdriver and Phillips (#1, #2 and #3) screwdrivers are also required.
Pins and springs have a tendency to fly out unexpectedly when building or maintaining your AR-15. It is recommended you wear safety glasses or goggles to protect your eyes.
In addition to the components needed to build your AR-15, there are other items you will need to have on hand for rifle maintenance.
Spare Parts Kit – This is handy to have during the initial build for any small parts that are dropped or lost, and again later for regular maintenance and repairs to your gun.
Cleaning Kit – This is an essential item for properly maintaining your rifle.
Ammo – For use on the range or hunting. When testing your rifle it is recommended you try several bullet types, weights, and powder charges to make sure the gun feeds a variety of ammunition properly.
Competitive AR-15 Builders Guide – This book contains detailed steps on how to properly assemble and disassemble your rifle. It also gives details on putting together a good toolbox and lists potential problems that can happen during a build. With a ring binding that allows it to lay flat on the workbench and over 750 photographs of the steps for all four AR-15 builds, this book is a workshop “must-have.”
How to Build an AR-15: Necessary Components
The parts needed to build your AR-15 will be based on what your rifle will be used for — hunting, tactical shooting, or target shooting. The purpose of the rifle affects every part’s decision you make.
You need to determine the gun caliber. Options range from 9x19mm pistol setup, a 300 blackout setup, or a 7.62x39mm AK setup. Please note that if you want a .308 caliber rifle you will need a different lower receiver because the AR-15 was never made for 3.08. An AR-10 is the .308 version of this rifle.
All components needed to build an AR-15 can be purchased online and shipped directly to a person’s home or business, with the exception of the lower receiver. The AR-15 lower receiver is considered the gun. You will need to provide the seller with a copy of an FFL (Federal Firearms License) and the address to the FFL.
You will pay the seller for the lower receiver and have it shipped to the FFL. When the gun shop receives the part you will fill out the ATF form so they can verify you are legally able to own a firearm. You pay the transfer fee and the AR-15 receiver is released to you.
If this is your first AR-15 build it is recommended you purchase some parts already assembled to make the build easier. One option would be to purchase either a pre-assembled upper receiver or a pre-assembled lower receiver.
There are different types of AR-15 builds, and the AR-15 parts needed will depend on those variations. The list below is for a typical M-4 style AR-15 with a stripped upper receiver and stripped lower receiver.
- AR-15 upper receiver
- Upper receiver parts kit
- AR-15 lower receiver
- Lower receiver parts kit – this includes the grip, trigger and assembly, magazine catch and release
- Lower receiver extension (a/k/a buffer tube)
- Buffer
- Buffer Spring
- Barrel and gas block/gas system (carbine length gas system is typical for this build)
- Handguards (length depends on what length gas system you choose on your barrel: carbine, mid-length, or rifle)
- Charging handle – what you use to cock the rifle
- Bolt carrier group — carrier, bolt, firing pin, cam, extractor, ejector, and spring
- Collapsible buttstock (or fixed if you prefer)
- Magazine — You will want at least one. Check state laws for magazine capacity limits. A 30 round magazine is a good, basic mil-spec magazine you can use to test the functionality of the rifle
Billet Lower Receiver or Forged Lower Receiver
Most AR-15 lower receivers are made to very specific tolerance levels based on military specifications (mil-spec). You can choose whichever AR-15 lower receiver has a roll-mark (logo) that you find most appealing. When selecting your lower receiver you will need to decide whether you want a billet or forged type.
A forged lower receiver has the metal “smashed” into the desired form while it is red hot. This compresses the metal and makes it very strong.
A billet lower receiver is machined from a single block of metal and has a more custom, aesthetically pleasing appearance. The billet style tends to have the trigger guard built-in so it is not removable.
It does not matter whether you purchase your receiver pre-assembled or stripped, in the eyes of the law the lower receiver is a gun and must be shipped to an FFL dealer.
Barrel Chamber and Barrel Twist
When selecting your barrel chamber, be aware that a rifle chambered for 5.56 can shoot both 5.56 and .223 ammunition. A rifle chambered for .223 can only shoot .223, it can not shoot 5.56.
When choosing a barrel twist ratio, choose one that matches the type of ammo you will normally be shooting. A 1.7 ratio means that when the bullet travels down the barrel it will make one complete spin (via riffling) for every seven inches it travels. The 1:7 ratio gives the option of shooting heavier rounds.
Law enforcement recommends a 1:9 ratio for plinking (informal target shooting) and a 1:7 ratio for hunting and home defense. The 55gr .223/5.56 is the most common bullet weight and the most frequently fired in both the 1:7 or 1:9 barrel twist.
When selecting your barrel, carbine, and mid-length or rifle length determines where the gas port in the barrel is placed. Carbine and mid-length gas systems normally are used on barrels of 16-18 inches or shorter. Barrels that are 20 inches or longer have a rifle length gas system.
You need to know what length gas system your barrel has. The gas tube will need to be the correct length to fit the gas system properly.
Should You Buy or Build
It can be less expensive to build your own AR-15, but if you do not have gunsmith skills or build experience it can be challenging. Many enjoy the knowledge that they have built their own AR-15 from scratch. The important thing is to make sure that when learning how to build an AR-15 you choose quality parts, take your time, and follow the steps precisely.